A prior art elevator car 12 (FIG. 1) includes a cab 13 rigidly disposed within a frame extending beneath a cross head 14 suspended by steel ropes 15 from a motor driven sheave (not shown). The frame of the car 12 includes two or more vertical stiles 19 extending from the cross head 14 to one or more planks 20 at the bottom of the car. A plurality of guides 21 position the elevator car with respect to a pair of hoistway rails 22 which are disposed to a building by brackets, in the known fashion. Each of the guides 21 typically comprise two or three wheels so as to provide guiding support in the front-to-back direction (into and out of the page as viewed in FIG. 1) as well as in the side-to-side direction (right to left as viewed in FIG. 1). Typically, there will be four guides 21 as seen in FIG. 1.
In the prior art, the guides 21 may be passive, meaning they have only spring and dashpot dampening on each of the wheels so as to smooth the ride. Guides of this type are shown, for example, in Skalski et al U.S. Pat. No. 5,117,946. On the other hand, the guides 21 may be active as shown in Skalski and Traktovenko U.S. patent application Ser. No. 08/021,649, filed Feb. 16, 1993, a continuation of Serial No. 07/731,185, filed Jul. 16, 1991, the subject matter of which is also shown in European Patent Application Pub. No. 0 467 673 A2. Active guides include actuators which can move the car 12 fore and aft as well as right and left to compensate for deviations in the rails 22 from straight vertical lines or planes in inertial space, and for other forces on the car. In elevators of the type shown in FIG. 1, it has been known to use electromechanical actuators and electromagnetic actuators for compensation. Such systems are generally extremely complicated and thus far have met with limited success. The actuators may be driven by a controller 24 in response to previously-recorded maps of the incremental positioning of the rail throughout the hoistway, to accelerations of the car 12 from sensors 25, 26 on the top and bottom of the car, and to a variety of other indications of the deviation of the rail or the motion of the car. However, variations in car position are also due to loading within the car 12, interference in stabilizing the car position with respect to one rail as a consequence of contemporaneously attempting to stabilize position with respect to the other rail, car oscillation and other noise. A significant problem is that the amount of correction which can be provided with present day safety devices is severely limited by the clearance (only a few millimeters) between the safety blocks and the rails. This provides less than adequate room within which to compensate for rail deviation and car motion.
In FIG. 2, another type of prior art elevator car 12, sometimes referred to as a "pendulum cab", has the cab 13 disposed on a platform 28 which is suspended by rods 29 from side frames 30 that extend fore-and-aft of the cross head 14 and are suspended from the cross head 14 by means of the stiles 19, or otherwise. Typically, there are four rods 29, one near each corner of the cab 13, which engage side frames 28a, 28b of the platform 28. The pendulum suspension tends to isolate the cab 13 from the jostling and vibration induced on the car by the rails 22. However, there is a tendency for the cab 13 to oscillate as a consequence of repetitive accelerations imparted thereto within the oscillatory frequency band of the rod suspension. In order to reduce the oscillations, compensation 31, such as damping, is typically provided between the platform 28 and the plank 20. The damping may be simple elastomeric supports, or may be spring/dashpot damping designed to minimize the effects at particular frequencies, as in Salmon et al U.S. Pat. No. 4,899,852.
Instead of just damping between the platform 28 and the planks 20, the cab 13 may be actively guided by the compensation 31 so as to have less lateral (side-to-side) movement, utilizing electromechanical or electromagnetic systems similar to those used for guiding the car as described with respect to FIG. 1. However, the active or passive control of lateral vibration of a cab suspended in the frame is simpler than guiding the car with respect to the rails because the cab has no relative vertical motion with respect to the frame of the car. In the aforementioned European Publication, there is disclosed a plurality of electromagnetic actuators which include C-shaped cores with electric coils on them operating against ferromagnetic reaction plates. In essence, the plates are disposed on the platform 28 and the electromagnets are disposed on the plank 20. The use of active electromagnetic actuators in a pendulum car of the type shown in FIG. 2 is well suited to counteract not only side-to-side oscillations and vibrations induced to the cab through the frame by the rails, but also forces (including torsional forces) acting directly on the suspended cab including wind forces (from the passage of adjacent elevators), passenger motion within the cab, and otherwise. The problem with such a system is that the electromagnetic actuators are pushing from the cab to the frame, which in turn reacts through the guides 21 to the rails 22. The frame is therefor spongy and the intended reaction is not achievable; and, some of the forces are reflected back through the guides to the frame.